1. Field of The Invention
The present invention concerns a drive for a motor vehicle, and particularly for a tractor with an internal combustion engine and at least one attached gearbox having a drive shaft to drive the front and/or rear wheels.
2. Description of the Related Art
Gearboxes are frequently used in motor vehicles with internal combustion engines to allow varying speeds with optimum power output. Supplemental gearboxes, such as auxiliary transmissions and creeper gearboxes, are in use today in addition to primary shifted gearboxes to provide extremely high ratios of operating speeds, as may be required, for example, in agricultural vehicles.
In agricultural tractors in particular, an extremely slow drive often is needed, for example, in planting, which may require several speeds between 0 and 2 km/hour. For such slow speeds, creeper gearboxes are used. Unfortunately, due to the relatively low rotational speeds involved, relatively large torques are developed, so that the creeper gearboxes must be relatively large, which is costly. In addition, conventional gearboxes, including supplemental and creeper gearboxes, have the peculiarity that a stepless drive is not possible over large speed ranges. Furthermore, speeds that vary only slightly from 0 can be obtained only by slipping the clutch.